Double sealing is typically provided by placing two seals in the housing through which the shaft passes, each seal being adapted for the corresponding medium to be sealed, the seals being positioned one after another, with a space between them, in the axial direction.
In the case of injection pumps, double sealing is currently provided in a conventional way, using, on the one hand, a rubber ring on the oil side, and, on the other hand, a rubber or PTFE sealing ring with a “special pressure” profile on the diesel fuel side.
The two parts are assembled head-to-tail in the different housing diameters, and a channel is machined in the housing between the two rings to discharge liquid to the outside in case of leakage. This channel also serves to maintain atmospheric pressure in this area.
This solution, one embodiment of which is shown in FIG. 1, has two major limitations identified by the inventors: it requires a large overall axial length, of the order of 20 mm at least (or 18.5 mm at the very least), and requires a housing with two compartments having different diameters, each adapted to one of the two seals.
If compartments of different radial sizes are not provided, it may be impossible to ensure the precise positioning of the seals, including their positioning relative to one another, or to prevent obstruction of the discharge channel.